Power converter with self-driven synchronous rectifier control circuitry

1. A power converter comprising:

a first AC input terminal coupled between first and second synchronous rectifier switching elements, the first and second synchronous rectifier switching elements coupled across first and second DC output terminals;

a second AC input terminal coupled between third and fourth synchronous rectifier switching elements, the third and fourth synchronous rectifier switching elements coupled across the first and second DC output terminals;

an AC input sensing circuit;

a DC level shifting circuit effective to apply a DC offset to an AC input signal received via the sensing circuit; and

switching control circuitry coupled to receive the AC input signal with the DC offset and comprising

a first comparator circuit effective to compare the AC input signal with the DC offset to a first reference voltage and to generate a first control signal for turning on the first and fourth switching elements when the input signal is greater than the first reference voltage, and

a second comparator circuit effective to compare the AC input signal with the DC offset to a second reference voltage and to generate a second control signal for turning on the second and third switching elements when the input signal is less than the second reference voltage.

2. The power converter of claim 1 , wherein the positive half cycle and the negative half cycle of the AC input signal are defined with respect to the DC offset.

3. The power converter of claim 1 , the synchronous rectifier switching elements comprising MOSFET rectifiers.

4. The power converter of claim 3 , the synchronous rectifier switching elements further comprising parallel diodes.

5. The power converter of claim 1 , wherein the first and second reference voltages are substantially equal to the DC offset.

6. The power converter of claim 1 , further comprising a first high side driver circuit effective to receive the first control signal and to generate an electrically isolated gate drive signal for turning on the first switching element, and a second high side driver circuit effective to receive the second control signal and to generate an electrically isolated gate drive signal for turning on the third switching element.

7. The power converter of claim 6 , further comprising a first buffer drive circuit coupled to receive the first control signal and to generate a gate drive signal for turning on the fourth switching element, and a second buffer drive circuit coupled to receive the second control signal and to generate a gate drive signal for turning on the second switching element.

8. A power converter comprising:

a first AC input terminal coupled between first and second synchronous rectifier switching elements, the first and second synchronous rectifier switching elements coupled across first and second DC output terminals;

a second AC input terminal coupled between third and fourth synchronous rectifier switching elements, the third and fourth synchronous rectifier switching elements coupled across the first and second DC output terminals;

an AC input sensing circuit;

a first comparator switching element coupled to the sensing circuit and configured to be turned on during a positive half cycle of the AC input signal;

a second comparator switching element coupled to the sensing circuit and configured to be turned on during a negative half cycle of the AC input signal;

a first driver circuit effective to generate drive signals to turn on and off the first and second synchronous rectifier switching elements in accordance with on-states of the first and second comparator switching elements, respectively; and

a second driver circuit effective to generate drive signals to turn on and off the third and fourth synchronous rectifier switching elements in accordance with on-states of the second and first comparator switching elements, respectively.

9. The power converter of claim 8 , wherein a threshold value for the comparator switching elements defines a DC offset for referencing the positive and negative half cycles of the AC input signal.

10. The power converter of claim 8 , the synchronous rectifier switching elements and the comparator switching elements comprising MOSFETs.

11. The power converter of claim 10 , the synchronous rectifier switching elements further comprising parallel diodes.

12. The power converter of claim 8 , the AC input sensing circuit comprising a first pair of resistors coupled on a first end to the first AC input terminal and on a second end to circuit ground, and a second pair of resistors coupled on a first end to the second AC input terminal and on a second end to circuit ground.

13. The power converter of claim 12 , the first comparator switching element having a source terminal coupled to circuit ground and a gate terminal coupled to a drain terminal of the second comparator switching element and further to a node between the second pair of resistors, and

the second comparator switching element having a source terminal coupled to circuit ground and a gate terminal coupled to a drain terminal of the first comparator switching element and further to a node between the first pair of resistors.

14. The power converter of claim 8 , further comprising a diode bridge rectifier coupled on a first end between the AC input terminals and on a second end between the first and second DC output terminals.